1. Field of the Invention
The present invention relates to a lens-fitted photo film unit and a sprocket wheel for the same. More particularly, the present invention relates to a sprocket wheel used with a photo film in which perforation sets are arranged and each of them includes two perforations, and a lens-fitted photo film unit incorporating the sprocket wheel.
2. Description Related to the Prior Art
There is a photo film cassette of the IX240 type, which has a cassette shell which is plastic and smaller than that of 135 type. Photo film of this type has a perforation train, which consists of a train of numerous perforation sets. Each of the perforation sets includes two perforations arranged at a small interval, and is associated with one frame. As is well-known, the IX240 type is consistent with the Advanced Photo System (trademark). Products for use with this type of photo film cassettes include a compact camera and a lens-fitted photo film unit, which is sold for example with a trade name of Fujicolor Quick Snap Super Slim (manufactured by Fuji Photo Film Co., Ltd.).
The lens-fitted photo film unit incorporates a photo film advancing device, in which a sprocket wheel is used. The sprocket wheel has two pairs of teeth, which are arranged on the peripheral face in a rotationally symmetrical manner. In the photo film, there are sections without perforations between two adjacent ones of the perforations arranged at a longer interval. There occurs a temporary state where none of the teeth on the sprocket wheel is meshed with the perforations. However one of the teeth on the sprocket wheel succeeding to a tooth having been meshed is moved to a position where it can be meshed with a succeeding one of the perforations, because the photo film advancing device has a plate spring which pushes a cam member disposed coaxially with the sprocket wheel. The cam member rotates in a direction of rotation of the sprocket wheel. The rotation of the cam member also causes a shutter to be charged and a counter wheel to indicate information of the number of remaining available frames.
The known example of the photo film advancing device has a shortcoming in that a photo film winder wheel requires much rotating force to be rotated, because the plate spring pushes the cam member forcibly. If it is conceived to reduce the biasing force of the plate spring, then the sprocket wheel can be rotated only by the reduced force. Next one of the teeth does not move sufficiently to a position of contact with the photo film. Failure is likely to occur in mesh of the sprocket wheel with the perforations. To solve this problem, there is a suggested improvement of the photo film advancing device in which a circular body of the sprocket wheel having the teeth has a relatively great radius, and a longer peripheral portion between the teeth is pressed against the photo film for the purpose of rotating the sprocket wheel with frictional force of the photo film.
In the sprocket wheel above, the frictional force considerably varies in accordance with a position of the photo film relative to the sprocket wheel. If the frictional force is low, there occurs failure in the rotation of the sprocket wheel. If the frictional force is high, it is likely that there occur scratches of the photo film or pressure fogging to the photo film.
In view of the foregoing problems, an object of the present invention is to provide a sprocket wheel which is used with a photo film, and can be reliably meshed with the photo film and rotated thereby, the photo film having perforation sets arranged in a train, each of the perforating sets including two perforations, and to provide a lens-fitted photo film unit incorporating the sprocket wheel.
Another object of the present invention is to provide a lens-fitted photo film unit in which dust proofness and/or light-tightness along juncture between plural parts of its body is increased.
In order to achieve the above and other objects and advantages of this invention, a sprocket wheel is adapted to be rotated by movement of photo film, the photo film having plural perforation sets arranged along one edge thereof in line at a regular pitch, each of the perforation sets including first and second perforations, the first and second perforations being arranged closely at a regular distance. The sprocket wheel has a wheel body. At least one tooth set includes first and second teeth, disposed to protrude from a peripheral face of the wheel body, respectively for being meshed with the first and second perforations serially. A contact portion is disposed on the peripheral face of the wheel body, for frictionally contacting a portion of the photo film between first and second perforation sets, to be rotated by the movement of the photo film, the first and second perforation sets being included in the plural perforation sets and adjacent to each other, the tooth set being meshed with the second perforation set after being disengaged from the first perforation set.
In a preferred embodiment, a gap is formed in the wheel body, is open in the peripheral face of the wheel body, for defining a flap shape of the contact portion in the peripheral face, and movement of the photo film is frictionally transmitted to the contact portion while the contact portion is shifted thereby toward a rotational center of the wheel body.
The contact portion is so inclined that a radius thereof with reference to the rotational center increases on the peripheral face of the wheel body.
The second perforation is larger than the first perforation, and the second tooth is larger than the first tooth.
The at least one tooth set is two tooth sets disposed in respective positions rotationally symmetrical with reference to the rotational center.
The first tooth is disposed adjacent to the contact portion and outside the gap, and shiftable toward the rotational center.
A spring portion is disposed in the gap, for receiving the contact portion when the contact portion is pressed by the photo film, for limiting a shiftable range of the contact portion shiftable toward the rotational center.
The contact portion includes a press surface for contacting the photo film, the press surface being inclined with reference to a direction of a thickness of the wheel body.
The sprocket wheel is incorporated in a lens-fitted photo film unit. The lens-fitted photo film unit includes a photo film supply chamber for containing a roll of the photo film. A cassette holder chamber contains a photo film cassette, to wind the photo film therein from the photo film supply chamber, the photo film passageway being formed to extend between the photo film supply chamber and the cassette holder chamber.
Consequently the sprocket wheel can be reliably meshed with the photo film and rotated thereby.
In still another preferred embodiment, a lens-fitted photo film unit is pre-loaded with photo film for taking an exposure thereon, the lens-fitted photo film unit including first and second parts of plastic, and a claw and a claw receiver portion, retained on each other, for connecting the first part to the second part. The lens-fitted photo film unit includes a resilient push plate, formed integrally with the first part to protrude toward the second part, having a length greater than an interval between the first and second parts being connected together, resiliently flexed by contact with the second part, for pushing the second part in a direction away from the first part, so as to tighten retention between the claw and the claw receiver portion.
The push plate is shaped with a thickness decreasing toward the second part.
A first wall is formed on the first part, and confronted with the second part, the push plate being disposed on the first wall. A second wall is formed on the second part, positioned substantially in parallel with the first wall when the first and second parts are connected together, and contacted by the push plate.
A claw plate is disposed on the first wall to protrude toward the second wall, and having the claw disposed on an end thereof. A receiver plate is disposed on the second wall to protrude toward the claw plate. The claw receiver portion is a receiver opening, formed in the receiver plate, for retaining the claw by receiving the claw.
A first ridge is disposed on the second wall to protrude toward the first wall, and extended close to an edge of the second wall. A second ridge is disposed on the second wall to protrude toward the first wall, and extended along the first ridge, the push plate being disposed between the first and second ridges, for preventing ambient light from entry between the first and second walls.
A photo film holder unit contains the photo film. A front cover covers a front of the photo film holder unit. A rear cover covers a rear of the photo film holder unit, to prevent ambient light from being incident upon the photo film. The first and second parts include the photo film holder unit and the rear cover.
The first part is the rear cover, and the second part is the photo film holder unit.
Consequently dust proofness and/or light-tightness along juncture between plural parts of its body is increased.